Data processing installations that use direct access storage devices (DASD), such as disk file storage subsystems that store binary data on floppy or rigid magnetic or optical recording disks, many times experience data processing problems such as slow response time and/or poor data availability. Slow response time may be caused by one disk file being accessed most of the time, while the other disk files are used only infrequently. Poor availability of data may be caused by one disk file having recurring errors, or by a disk file being out of commission due to a malfunction. As a result, the data processing industry often resorts to backing up frequently used data on-line, or the data may be redistributed to other disk files.
As the price of DASD files has dropped over the years, the concept of packaging more than one disk spindle in a common housing or box has been developed. With such a storage subsystem packaging scheme, more efficient data processing operation is possible. For example, it is usually desirable to limit the data storage capacity that is contained under any one disk access arm. Since the density of disk data storage has increased markedly, and is continuing to increase, each spindle of a multiple spindle device can be made of a small physical size, thus facilitating the packaging of a number of these small spindles in one physical housing.
The present invention makes use of a number of such a multiple spindle, unitary, DASD devices to form optimized forms of data storage, including the mirroring of data files and the interleaving of data files.
As a feature of the invention, a direct access storage device subsystems may comprise a number of separate physical housings, each housing having a number of disk supporting spindles mounted therein.
U.S. Pat. No. 3,864,750 is of interest relative thereto in that this patent describes a magnetic disk system that includes four packs of magnetic disks having a single rotary head access mechanism positioned in the middle of the disk packs. However, in this device all four disk packs are driven by a single motor and a single timing belt, and thus the variable rotational spindle position of the present invention cannot be achieved.
As a feature of the invention, a direct access storage device subsystem may comprise a number of separate and individual disk drives or files, wherein for purposes of data integrity the data is mirrored by writing the same data to common addresses of each disk drive.
U.S. Pat. No. 4,722,085 is of interest relative thereto in that this patent describes a magnetic disk storage system having a number of disk files wherein data is written in parallel to a common addressed sector location on each of the disk files. However, in this device each disk file operates independent of all other disk files within the system, and no provision is made to provide an optimum positional relationship between the location of the addressed disk sector and the accessing heads of the various disk files.
The publication Electronic Design, Nov. 12, 1987, at pages 45-46, is also of interest in that it describes a disk drive system in which five spindle-synchronized disk drives are used to store data. Data is stored on four of the disk drives by way of simultaneous parallel data transfer. The fifth disk drive is used as a parity drive. The fifth drive may also be used to replace failed data drive, if such a failure should occur.
A feature of the invention provides for servo control among the spindles of a multiple spindle DASD unit. In this connection, it is known that others have linked a number of disk drives using a phase locked loop feedback mechanism. In this way, the rotation of two or more disk drives was synchronized so that data could be written to or read from multiple drives quickly. Deskewing logic was required in the disk drive controller in order to implement this feature. (Electronic Engineering Times, page 10, Oct. 5, 1987)
As a feature of the invention, mirrored data files are stored on the disks of a multiple spindle DASD device in a positionally staggered relationship, such that response time and/or data availability is improved.
In the unrelated art of change coupled device (CCD) data storage devices, means have been provided to reduce the mean access time to data storage blocks by moving the most likely next block of data to be accessed to an optimum position for accessing. U.S. Pat. No. 4,400,793 is an example.
Use of the present invention also enables the interleaving of data among the disks of a multiple spindle DASD unit. Data interleaving is old per se, as is exemplified by the magnetic tape storage means describes in U.S. Pat. Nos. 2,794,006 and 4,222,078 for example.
While others have attempted to provide more efficient use of DASD subsystems by a data processing system, there remains a need to provide yet greater improvement in DASD response time and/or DASD data availability.